The present invention relates to a substrate processing method and apparatus for use in a semiconductor device, a liquid crystal display and the like. More specifically, the present invention relates to a method and apparatus for processing a substrate by using a liquid agent.
In the semiconductor device and liquid crystal display, desired functions can be imparted by applying various types of processing to a substrate and forming a micro pattern on the substrate. To process the substrate as mentioned above, not only a dry process using a gas but also a wet process using a liquid agent is widely employed. The wet processing is performed to develop a photosensitive resist pattern, which will be used to form a micro pattern.
To form a photosensitive resist pattern, a photosensitive resist is applied on a film which has been formed on a silicon or quartz substrate, thereby forming a photoresist film. An exposure mask is placed above the photoresist film. Light is applied through the mask, whereby a desired region of the resist film is exposed to light. Subsequently, the light-exposed portion of the resist film, if the resist film is a positive type one, or the non light-exposed portion, if the resist film is a negative type one, is removed with an organic solvent or an aqueous alkaline solution. As a result, a photosensitive resist pattern is formed.
To form a chromium mask for use in light exposure, the wet process is applied. After the chromium film is formed on a substrate, a photosensitive resist pattern is formed. Those parts of the chromium film which are not covered with the resist pattern are isotropically removed by the wet-etching using a ceric nitrate ammonium solution.
To remove unnecessary organic materials from a substrate prior to processing, or to remove the photosensitive resin pattern from a substrate after completion of etching, a mixed liquid agent consisting of sulfuric acid and hydrogen peroxide is used.
If a silicon substrate is reacted with oxygen contained in the air, a native oxide film will be formed. Since the native oxide film prevents uniform processing, it must be removed. To remove the native oxide film, a liquid agent such as NH.sub.4 or diluted HF is applied.
In the case where a gold film is formed on a silicon substrate, an Au plating solution is used.
Wet processing methods include a dip treatment in which the substrate is dipped in a liquid agent, and a puddle treatment in which the substrate is treated with a liquid agent supplied to the main surface of the substrate. However, the dip treatment has problems in that a large amount of the liquid agent is required and in that the substrate may be contaminated with a material present in the rear surface. Because of the problems, the paddle treatment tends to be widely employed rather than the dip treatment. To perform the puddle treatment, the substrate is fixed at the back by a vacuum chuck (Jpn. Pat. Appln. KOKAI Publication No. 7-235473).
In the wet treatment, the treatment is performed through a chemical reaction between a liquid agent and the film to be treated. As the treatment proceeds, the concentration of reaction products increases, whereas that of the starting liquid agent decreases. Since the reaction products and the starting liquid agents do not diffuse immediately, their concentrations varies locally. Consequently, the surface of the film cannot always be processed uniformly.
In a developing method, for example, resist is removed from a desired region of the substrate with an aqueous alkaline solution and is dissolved by a neutralization reaction with the developer (aqueous alkaline solution). This is because the resin forming a resist removal region has an acidic group such as a carboxylic acid or a phenol group as a side chain. The substrate is brought to a standstill in a conventional development step, so that the dissolved resin diffuses slowly. As a result, the dissolved resin is left near the resist removal region. In addition, an OH group does not diffuse sufficiently fast. The concentration of the OH group is therefore locally low after the OH group is consumed in the neutralization reaction. This reduces local pH. The volume of the resin in the removal region, i.e., the amount of the resin to be dissolved, depends on a pattern. Hence, the dimensions of the photosensitive resist finally left on the substrate surface is not uniform.
Then, the aforementioned publication No. 7-235473 discloses the following method using a rotation-type resist developing apparatus. In this apparatus, a capillary action is induced in the treatment solution between the wafer and the liquid agent supply board located in proximity of the wafer. The time required for dispersing the treatment solution over the resist film can, therefore, be reduced by the capillary action and thereby uneven development decreases. However, in this method, development is carried out at a predetermined time interval after the developer is dispersed over the entire surface of the resist film. Thus, the local change in pH of the developer inevitably occurs, as mentioned above.
In the case where the developing process is performed while stirring the developer, an ultrasonic oscillator is employed as disclosed in a method of Jpn. Pat. Appln. KOKAI Publication No. 57-208134. However, when the ultrasonic oscillator is used, voids are produced or destroyed in the liquid agent by the cavitation effect due to the oscillation. Since the substrate has larger acoustic impedance than the liquid agent, the void tends to form, especially on the substrate. Due to voids, the liquid agent does not always contact the substrate. As a consequence, the substrate surface cannot be processed uniformly.